Pre-cut plating lines on lead frames and laminate substrates for saw singulation

ABSTRACT

Described herein is a technology or a method for pre-fabricating pre-cut plating lines on a lead frame with use of a pre-cut etchback process to minimize burrs during a semiconductor package singulation process. A package includes: a chip, and a lead frame that mounts the chip. The lead frame further includes pre-fabricated pre-cut plating lines that are etched back on the lead frame to form an opening slot on a periphery of the lead frame. The opening slot allows a saw blade to cut through a prepreg material, without touching or cutting a conductive material of the lead frame.

BACKGROUND

A semiconductor package is a metal, plastic, glass or a ceramic casingthat includes electronic components. Individual discrete electroniccomponents are etched in a silicon wafer. The process of assembling asemiconductor package includes cutting a wafer and assembling the waferin a semiconductor package. The semiconductor package provides componentand circuit protection against exposure to extreme temperatures andagainst impact and corrosion. The semiconductor package also holdscontact pins or leads.

BRIEF DESCRIPTION OF THE DRAWINGS

The detailed description is described with reference to accompanyingfigures. In the figures, the left-most digit(s) of a reference numberidentifies the figure in which the reference number first appears. Thesame numbers are used throughout the drawings to reference like featuresand components.

FIG. 1 illustrates an example semiconductor package that implementspre-cut plating lines to minimize burrs as described herein.

FIG. 2 illustrates an example of a semiconductor package with etchedback pre-cut plating lines to minimize burrs as described herein.

FIG. 3 illustrates an example implementation of a cross-section of amulti-layer semiconductor package to minimize burrs as described herein.

FIG. 4 illustrates an example implementation of the pre-cut platinglines as described herein.

FIG. 5 illustrates an example implementation of pre-fabricating thepre-cut plating lines using pre-cut an etchback process as describedherein.

FIG. 6 illustrates an example implementation of chip singulation asdescribed herein.

FIG. 7 illustrates an example process chart illustrating an examplemethod for minimizing burrs during singulation of a semiconductorpackage using etched back pre-cut plating lines as described herein.

DETAILED DESCRIPTION

Described herein is a technology or a method for fabricating pre-cutplating lines using a pre-cut etchback process in order to minimizeburrs during a semiconductor package singulation process. Plating linesare lines, such as copper lines, that are used for electroplating. Priorto an assembly process, plating lines are precut using an etch backprocess. For example, a chip is mounted on a lead frame. Pre-cut platinglines are etched back on the lead frame (or laminate substrate) duringfabrication of the lead frame and prior to mounting of the chip.

In an embodiment, the pre-cut plating lines form an elongated openingslot on a periphery of the lead frame. The elongated opening slot formsa “U” shape. A bottom of the formed “U” shaped opening slot includes anexposed surface of a prepreg material. In certain implementations,prepreg or pre-impregnated material is a glass fiber impregnated withresin used to stick a core and copper foil together in a laminatesubstrate fabrication. During chip singulation, through use of a sawblade, the saw blade is aligned onto the formed “U” shape withouttouching or cutting an etched back copper portion of the lead frame. Thecopper portion includes copper plating lines of the lead frame. The sawblade cuts through the prepreg material without touching the copperplating lines of the lead frame, and minimizing burrs.

FIG. 1 is an example semiconductor package 100 (or device) thatimplements pre-cut plating lines to minimize burrs as described herein.The pre-cut plating lines are formed on a lead frame (or also calledlaminate substrate) through an additional semiconductor fabrication stepof etching back an opening slot or a cavity on the lead frame. In thisexample, the etched back opening slot or cavity facilitates minimizationof burrs (i.e., burrs in copper) during chip singulation.

As depicted, the package 100 includes a lead frame 102, and a pluralityof semiconductor chips (or dies) 104A-104B. The first chip 104A sits ona first copper mounting material 106A, while the second chip 104B sitson a second copper mounting material 106B. The package 100 further showsbonding wires 108 that connect the chips 104 to multiple leads 110.

Furthermore still, plating lines 112 are patterned on the lead frame 102to connect or extend electrical connections of the bonding wires 108towards edges of the lead frame 102. The patterned plating lines 112 andlead 110 include a layer of conductive materials such as coppermaterials that are laminated on top of an insulating material 114. Theadditional etchback process as described herein includes pre-fabricationof a pre-cut plating line or a trench that traverses the plating lines112 prior to chip singulation. As shown, the plating lines 112 and thebonding wires 108 are illustrated to include simple configurations forpurposes of describing the implementations herein.

The package 100, for example, is a Quad Flat No-leads (QFN) package, aplastic ball grid array (PBGA), or a land grid array (LGA) package thatis ready for singulation with a dicing device in order to separate thechip 104A from the chip 104B. The QFN package, the PGBA, and/or LGApackage physically and electrically connects the chips 104A and 104B tothe lead frame 102 through a surface-mount technology. In other words,the chips 104 are connected to surfaces of the lead frame 102 withoutuse of through-holes.

The dicing device can include a rotating blade that is configured to cutthrough a singulation line 116 to form a first package and secondpackage. These packages include the first chip 104A and second chip104B. During the process of separating the packages, burrs or copperburrs from the plating lines 112 along the singulation line 116 canaffect performance of the package. Burrs are deformations of metals,such as the copper that is implemented, resulting in undesired metalthat causes shorting to the adjacent metal (i.e. copper) during thesingulation process. Similarly, copper burrs from other edges of thelead frame 102 can result due to singulation of the other sides or edgesof the lead frame 102.

Copper burrs from the cut portions of the plating lines 112 on each sideof the singulated package can provide an undesired short circuit to thefirst chip 104A or second chip 104B. In this example, pre-cut platinglines (not shown) using pre-cut etchback process are formed and disposedon a periphery of the first and second packages in order minimize oravoid presence of the undesired copper burrs during singulation of thelead frame 102 to form separate packages.

In an embodiment, the lead frame 102 is made of a copper material thathas been plated with solder, AuNi or palladium. These copper materialsare laminated onto the insulating material 114 and thereafter, thecopper materials are patterned to form the plating lines 112 and thelead 110. For example, the lead 110 include electrodes or conductivetracks that are laminated to the insulating material 114. In thisexample, the leads 110 interconnect the bonding wires 108 and theplating lines 112.

Similarly, the copper mounting materials 106 are formed to providemechanical and electrical support to the chips 104. These coppermounting materials 106 further provides structural protection to thechips 104 during the singulation process.

FIG. 2 is an example semiconductor package 200 with etched back pre-cutplating lines to minimize burrs as described herein. The semiconductorpackage 200 is a package with different layers as shown.

As depicted, a top view of the semiconductor package 200 includes thefirst chip 104A, the copper mounting material 106A, bonding wires 108,the plating lines 112 that extend from the lead 110 to outer perimeteror periphery of the lead frame 102, vertical singulation lines 202A and202B, and horizontal singulation lines 204A and 204B. Furthermore, thetop view includes etched back vertical pre-cut plating lines 206A and206B, etched back horizontal pre-cut plating lines 208A-208B, and across-section 210. The cross-section 210 (below the top view) furtherillustrates additional components and configurations of thesemiconductor package 200.

In an embodiment, each of the vertical pre-cut plating lines 206includes etched longitudinal opening slot that aligns with thecorresponding vertical singulation line 202. The vertical singulationline 202A is disposed along a longitudinal center line of the etchedback vertical pre-cut plating line 206A. In this example, the etchedback vertical pre-cut plating line 206A includes a “U” shaped openingslot or trench cross-section on a periphery of the lead frame 102. Theperiphery can be near or along the edges of the lead frame 102.Furthermore, the etched back vertical pre-cut plating line 206A includesa length sufficient to traverse or cut across all plating lines 112along the side of the lead frame 102 where the etched back verticalpre-cut plating line 206A is located.

Similarly, the etched back vertical singulation line 202B is disposedalong a longitudinal center line of the vertical pre-cut plating line206B. In this case, the vertical pre-cut plating line 206B includes theopening slot formed using the pre-cut etchback process on opposite sideof the vertical pre-cut plating line 206A. Furthermore, the etched backvertical pre-cut plating line 206B includes a length sufficient totraverse or cut across all plating lines 112 along the side of the leadframe 102 where the etched back vertical pre-cut plating line 206B islocated.

The foregoing descriptions regarding the etched back verticalsingulation lines 202A-202B are similarly applicable to the etched backhorizontal pre-cut plating lines 208A-208B. That is, the etched backhorizontal pre-cut plating lines 208A-208B include opening slots thatare formed on the periphery of the lead frame 102. Each of these openingslots or trenches includes a length sufficient to traverse or cut acrossall plating lines 112 along the side of the lead frame 102 where theetched back horizontal pre-cut plating lines 208A-208B arecorrespondingly located.

In an embodiment, the etched vertical pre-cut plating lines 206A-206Band the horizontal pre-cut plating lines 208A-208B above are formed toavoid presence of burrs during a package singulation process. Thepresence of opening slots or trenches traversing the plating lines 112prevent the burrs from occurring since the width of the trenches canaccommodate the saw blade without the saw blade touching or cuttingthrough the copper materials of the plating lines 112. These openingslots are implemented during the fabrication of the lead frame 102. Inother words, prior to the processes of mounting of the chips 104 to thelead frame 102, connecting of the bonding wires 108, and sealing ofresins (not shown) prior to the singulation process, the opening slotsfor the vertical and horizontal singulation lines are pre-fabricatedusing the pre-cut etchback process on the lead frame 102.

Referencing the depicted cross-section 210 (i.e., cross-section of thetop-view), the first chip 104A sits on the first copper mounting area106A. The cross-section 210 further shows the etched vertical pre-cutplating lines 206A-206B on top surface of the lead frame 102, andvertical pre-cut plating lines 206C and 206D on a bottom surface of thelead frame 102. Furthermore still, the cross-section 210 shows prepregmaterial 212 that bonds the top and bottom materials (e.g., copperlaminated layer) of the lead frame 102. Bonding material 214, such assolder balls are also shown at the bottom of the lead frame 102 toconnect the first package (i.e., first chip 104A package) to anotherpackage (e.g., singulated second chip 104B package).

In an embodiment, the opening slots defined by the pre-cut plating lines206A and 206C of the cross-section 210 are aligned with one another.That is, the pre-cut plating line 206A is symmetrical to the pre-cutplating line 206C. Furthermore, each of the pre-cut plating lines 206Aand 206C is formed as an elongated tube or cavity etched out from thecorresponding top and bottom surfaces of the lead frame 102. In thismanner, a cutting plane can be formed along the longitudinal centerlines of the pre-cut plating lines 206A and 206C. In other words, thecutting plane extends from a longitudinal center line of the pre-cutplating line 206A to an opposite longitudinal center line of the pre-cutplating line 206C at the bottom lead frame 102. Furthermore, the sawblade that passes through this cutting plane will cut through theprepreg material 212 but will not touch the plating lines 112.

Similarly, the etched opening slots defined by the pre-cut plating lines206B and 206D are aligned with one another. That is, the pre-cut platingline 206B is symmetrical to the pre-cut plating line 206D. Furthermore,each of the pre-cut plating lines 206B and 206D is formed as anelongated tube or cavity that is etched back from the corresponding topand bottom of the lead frame 102. In this manner, the cutting plane isformed along the longitudinal center lines of the pre-cut plating line206B and extends to the longitudinal center lines of the pre-cut platingline 206D. Furthermore, the saw blade, which passes through this cuttingplane, will cut through the prepreg material 212 without touching theplating lines 112.

In an embodiment, the cross-sectional shapes of the opening slotsdefined by the pre-cut plating lines 206A to 206D can be elongated “U”shaped tubes or cavities. In another embodiment, the shape of theopening slot can be square shape, or any other shape as long as theetched opening slots allow the singulation blades to cut through thecutting planes without touching or cutting the copper materials of thelead frame 102 and particularly, the plating lines 112. In other words,a trench width (i.e., mouth of the “U” shaped tubes) is wider than awidth of the blade to be used during singulation.

As described herein, the prepreg material 212 include glue materials tobond the top copper laminated materials to the bottom copper laminatedmaterials of the lead frame 102. The prepreg material 212 can alsoinclude other materials in between to provide mechanical support to thelead frame 102 as further described below.

FIG. 3 illustrates an example cross-section 300 of a multi-layersemiconductor package to minimize the burrs as described herein. Themulti-layer semiconductor package, for example, includes the first chip104A mounted on the lead frame 102, and a second chip 302 mounted on thelead frame 304. In this example, the lead frame 304 includes a secondcopper mounting area 306 for the second lead frame 304. Furthermore, thebonding material 214 such as solder balls or solder bumps physicallyand/or electrically connects the lead frame 102 to the lead frame 304.Bonding material 214 attaches a backside of the first lead frame 102 tothe backside of the second lead frame 304.

As depicted, a portion of the cross-section 300 includes the pre-cutplating line 206A with a trench depth that is enough to expose materials(e.g., glue materials) of the prepreg materials 212A. The trench asshown is bounded by a prepreg surface 308A at the bottom, and trenchside walls 310A and 310B as the sides. The cross-section 300 furtherincludes a core material 312 disposed in between the prepreg materials212A and 212B, and pre-cut plating line 206C. The pre-cut plating line206C, as shown, is bounded by a prepreg surface 308B at the bottom, andside walls 314A and 314B at the side. The exposed material of theprepreg surface 308B can be glue materials, while the opening slot sidewalls 314A and 314B can be copper materials. The cross-section 300further includes a top solder-mask 316A layer and a bottom solder-mask316B layer.

In an embodiment, the opening slot pre-cut plating line 206A is etchedback to a certain depth such that the top surface (i.e., solder mask andcopper layer) are totally etched out and the prepreg material 212A isexposed. That is, the pre-etching of the lead frame 102 is performed toform the “U” shape to expose the prepreg surface 308A. In this manner,the singulation blade will pass in between the top sidewalls 310A and310B, cut through the prepreg material 212A, the core material 312, andthe prepreg material 212B; and thereafter exit through and in betweenthe bottom sidewalls 314A and 314B. The vertical singulation line 202A,as shown, illustrates the cutting plane for the singulation blade.

The portion of the cross-section 300 described above similarly apply toother sides of the first lead frame 102 and the second lead frame 304.As depicted, the pre-cut plating lines of the first lead frame 102 issymmetric to the pre-cut plating lines of the second lead frame 304.That is, the opening slots are pre-fabricated along the periphery oredges of the top and bottom surfaces of each of the lead frames 102 and304.

The core material 312 include materials to implement multi-layeredpackages. For example, the first chip 104A and the second chip 302 aredisposed as a stack. In this example, the core material 312, incombination with the prepreg materials 212A and 212B, can implement themulti-layered semiconductor package as described herein.

FIG. 4 illustrates an example implementation of the pre-cut platinglines as described herein. Particularly, FIG. 4 shows an exampleembodiment of the pre-cut plating line 206A formed on top of the leadframe 102.

As shown, the pre-cut plating line 206A can include an opening slotwidth of about 450 μm, which is measured from the trench sidewall 310Ato the trench sidewall 310B. For example, an opening slot 400 is thetrench width that includes a distance between the sidewalls 310A and310B. In this example, the opening slot 400 is also equal to an area ofexposed prepreg surface 308A. In other words, the etching or formationof the pre-cut plating line 206A includes removal of the solder mask316A, a conductive layer 402 (e.g., copper layer), and portions of theinsulating material 114 of the lead frame 102.

In an embodiment, the blade for the singulation as described herein inabout 300 μm in width. A saw line 404 can include the cutting plane forthe singulation blade. The saw line 404 can represent the verticalsingulation line 202A above.

For example, the opening slot 400 with a width of 400 μm, the saw line404 can be located at about 160 μm from the outer sidewall 310A. In thismanner, there is a width tolerance at both sides of the sidewalls 310Aand 310B in order to avoid burrs at the copper lead. The distance of oneside of the blade from the trench sidewall 310A is 10 μm, while anotherside of the blade has a distance of 140 μm from the other trenchsidewall 310B. In this example, the pre-cut plating line 206A willprevent any burrs from occurring in the plating lines 112 of the leadframe 102.

FIG. 5 illustrates an example implementation of pre-fabricating thepre-cut plating lines using the pre-cut etchback process as describedherein. As depicted, step 500 shows formation of a stack using theprepreg material 212A, the conductive layer 402 that is laminated on theinsulating material 114, and the solder mask 316A. Furthermore, the step500 illustrates a masking layer 502 that is patterned on the formedstack and particularly, on a top surface of the solder mask 316A to forma mask opening 504 on the solder mask 316A. The conductive layer 402 issimilar to the patterned plating lines 112 on the insulating material114.

The masking layer 502 can include different materials such asphotoresist, silicon nitride, and the like. Furthermore, the maskinglayer 502 is formed or patterned through a technique of spin-coating,chemical vapor deposition (CVD), low pressure chemical vapor deposition(LPCVD), etc. For example, the masking layer 502 is a layer ofphotoresist that is formed using traditional photolithography techniquesthat includes spin-on coating, soft-bake, exposure, hard bake anddevelop, etc.

In an embodiment, a width and length of the mask opening 504 define thewidth and length of the pre-cut plating lines as described herein. Forexample, the width of the mask opening 504 is the same as the widthbetween the trench sidewalls 310A and 310B of FIG. 4. In this example,the mask opening 504 can vary depending upon the application or desiresof a device designer.

At step 506, the pre-cut etchback process is performed to remove thelayer of solder mask 316A and the conductive layer 402. At step 506, theetching does not apply to portions of the solder mask 316A and theconductive layer 402 covered or protected with the patterned maskinglayer 502. Furthermore, the pre-cut etchback process is performed tototally etch out the unprotected or exposed solder mask 316A and theconductive layer 402. The exposed solder mask 316A and the conductivelayer 402 that is laminated on the insulating material 114 are locatedwithin an area defined by the mask opening 504. The total etching of thesolder mask 316A, the conductive layer 402 and the insulating material114 within the mask opening 504 will expose a top surface of the prepregmaterial 212A. For example, the top surface is the prepreg surface 308Aas shown in FIG. 3. In this example, the etching is limited to thicknessof the solder mask 316A layer and the conductive layer 402 plus theinsulating material 114.

In another embodiment, the pre-cut etchback process further cuts theconductive layer 402 such that the conductive layer 402 is not flushedon the sidewalls 310A and 310B as depicted in FIG. 4. The etched backsolder mask 316A and the prepreg surface 308A has the same trench widthof about 450 μm. The etched back conductive layer 402 has a trench widthof about 475 μm. In other words, the etching back of the conductivelayer 402 results to a wider width as compared to the exposed surface ofthe prepreg material, or to an opening width of the etched solder mask316A. In this regard, the conductive layer 402 is tucked in compared toprotruding solder mask 316A and as such, this etchback process furtheravoid occurrence of burrs on the conductive layer 402.

At step 508, the patterned masking layer 502 on the lead frame 102 isremoved. For example, a commercial chemical such as hydrogen peroxide(H₂O₂) is dispensed on a surface of the lead frame 102. The materials ofthe masking layer 502 reacts to the commercial chemical and dissolved.As a result, the pre-cut plating line is formed on the lead frame 102.For example, the formed pre-cut plating line is the pre-cut plating line206A as described in FIG. 2 above.

In an embodiment, the pre-fabrication of the pre-cut plating lines usingthe pre-cut etchback process above is applied to top and bottom surfacesof the lead frame 102. Furthermore, the configuration and shape of theetched back pre-cut plating lines can be of different shape andconfiguration other than the depicted straight lines. For example, theetched back shape includes half sphere, and right angle shapes, etc. Inthis example, the configuration and shape are implemented such that theetched back opening slot will traverse the plating lines 112 on the leadframe 102.

FIG. 6 illustrates an example implementation of chip singulation asdescribed herein. As shown, a singulation saw blade 600 moves up anddown within the etched back opening slot of the pre-cut plating line206B. In an embodiment, the blade 600 includes a width of about 300 μm,and is aligned to the cutting plane of the pre-cut plating line 206B. Inthis embodiment, the chip singulation can further use de-flashingprocessing step in order to remove the prepreg materials that are cutduring the process.

As shown, the etched back opening slot width of the pre-cut plating line206B is wider than the width of the singulation saw blade 600. In thisregard, the singulation saw blade 600 does not touch nor cut the leadframe 102 and particularly, the plating lines 112 of the packaging.

FIG. 7 shows an example process chart 700 illustrating an example methodfor minimizing burrs during singulation of a semiconductor package usingetched back pre-cut plating lines as described herein. The order inwhich the method is described is not intended to be construed as alimitation, and any number of the described method blocks can becombined in any order to implement the method, or alternate method.Additionally, individual blocks may be deleted from the method withoutdeparting from the spirit and scope of the subject matter describedherein. Furthermore, the method may be implemented in any suitablehardware, software, firmware, or a combination thereof, withoutdeparting from the scope of the invention.

At block 702, an etchback process is performed. The etchback process isparticularly performed to create pre-cut plating lines. The etch backprocess is performed by forming a stack of prepreg material 212A,conductive layer 402 that is laminated on the insulating material 114,and solder mask 316A. Patterning the masking layer 502 is then performedon the stack. Forming the mask opening 504 on top of the solder mask316A is then performed. Thereafter, the exposed or unprotected soldermask 316A and conductive layer 402 within the mask opening 504 areetched back to expose a top surface of the prepreg material 212A.Finally, the patterned masking layer 502 are dissolved with chemicals toproduce the pre-cut plating line on 206A on the lead frame 102. In anembodiment, the etched back pre-cut plating lines are formed on eachside in between chips, or on different locations of the lead frame 102depending upon the desired package configurations.

At block 704, mounting a chip or a plurality of chips on the lead frameis performed. For example, the chips 104A and 104B are mounted on thelead frame 102. In this example, the pre-fabricated pre-cut platinglines are formed on each side and in between chips, or on differentlocations of the lead frame 102 depending upon desired singulationlines.

At block 706, electrical connections from the chip to leads on the leadframe are made. For example, the electrical connections of the bondingwires 108 to leads 110 on lead frame 102.

At block 708, chip singulation on the lead frame is performed. In otherwords, cutting is performed through the pre-cut plating lines. Forexample, the first chip 104A is bounded by the vertical pre-cut platinglines 206A-206B and the horizontal pre-cut plating lines 208A-208B. Inthis example, the vertical singulation lines 202A-202B and thehorizontal singulation lines 204A-204B outline the singulation of thelead frame. That is, the saw blade 600 will pass and cut through thisoutline in order to avoid burrs during the singulation process toindividualize the packages.

What is claimed is:
 1. A method comprising: an etchback process on alead frame that comprises: forming a stack of prepreg material, aconductive layer, and a solder mask; patterning a masking layer on thestack; forming a mask opening on masking layer; etching back the soldermask and the conductive layer within the formed mask opening to expose atop surface of the prepreg material; and dissolving the masking layer,thereby creating pre-cut plating lines; mounting a chip on the leadframe; making electrical connections from the chip to leads on the leadframe; and cutting through the etched back pre-fabricated pre-cutplating lines.
 2. The method of claim 1, wherein the conductive layerincludes a copper layer that is laminated on an insulating material. 3.The method of claim 1, wherein each of the pre-fabricated pre-cutplating lines includes a “U” shaped opening slot.
 4. The method of claim3, wherein the opening slot includes a width wider than a width of a sawblade that is used for singulation.
 5. The method of claim 1, whereineach of the pre-fabricated pre-cut plating lines includes a length thattraverses the conductive layer on the lead frame.
 6. The method of claim5, wherein the conductive layer includes plating lines that extendelectrical connection of bonding wires from the chip.
 7. The method ofclaim 1, wherein each of the pre-fabricated pre-cut plating linesincludes a total etching of the conductive layer until the top surfaceof the prepreg material.
 8. The method of claim 1, wherein each of thepre-fabricated pre-cut plating lines includes a longitudinal openingslot that includes trench sidewalls and a surface of a prepreg material.9. A device comprising: a lead frame with a chip, wherein the lead framefurther comprises: a stack of prepreg material, a conductive layer, anda solder mask; pre-fabricated pre-cut plating lines that are etched backon the solder mask and the conductive layer of the lead frame, whereinthe pre-fabricated pre-cut plating lines include an etched back openingslot that exposes a top surface of the prepreg material.
 10. The deviceof claim 9, the pre-fabricated pre-cut plating lines includes a lengththat traverses the conductive layer on the lead frame.
 11. The device ofclaim 9, wherein each of the pre-fabricated pre-cut plating linesincludes a “U” shaped opening slot.
 12. The device of claim 11, whereinthe opening slot includes a trench width that is wider than a width of asaw blade that is used for singulation.
 13. The device of claim 9,wherein the conductive layer includes plating lines that extendelectrical connections of bonding wires to edges of the lead frame. 14.The device of claim 9, wherein the pre-fabricated pre-cut plating linesexpose the top surface of the prepreg material.
 15. The device of claim9, wherein each of the pre-fabricated pre-cut plating lines includes alongitudinal opening slot that includes trench sidewalls and the exposedtop surface of the prepreg material.
 16. The device of claim 15, whereina width of the exposed top surface of the prepreg material is the sameas the width of the opening slot.
 17. A semiconductor packagecomprising: a first chip mounted on a first lead frame; a second chipmounted on a second lead frame; a bonding material that attaches abackside of the first lead frame to a backside of the second lead frame,wherein each of the first and second lead frames further comprises: astack of prepreg material, a copper layer, and a solder mask;pre-fabricated pre-cut plating lines that are etched back on a peripheryof the lead frame, wherein the etched back pre-fabricated pre-cutplating lines include an etched back opening slot on the solder mask andthe copper layer, wherein the etched back opening slot exposes a topsurface of the prepreg material.
 18. The semiconductor package of claim17, wherein the pre-fabricated pre-cut plating lines expose the topsurface of the prepreg material.
 19. The semiconductor package of claim17, wherein each of the pre-fabricated pre-cut plating lines includes a“U” shaped opening slot.
 20. The semiconductor package of claim 17,wherein the opening slot includes a width that is wider than a width ofa saw blade that is used for singulation.